T-cell-mediated lympholysis as generated in vitro against trinitrophenyl-(TNP-) modified syngeneic murine spleen cells. The cytotoxic effectors generated are specific for both the modifying agent and for self major histocompatibility complex (MHC) products mapping in the K or D regions of the H-2 complex. Specificity of the effectors was such that they could not lyse H-2-matched targets in which the TNP group was presented on the targets by insertion of a TNP-fatty acid-dextran conjugate into the cell membrane. However, effectors could be generated by culturing spleen cells with TNP coupled to soluble proteins. Cellular analyses of the mechanism by which TNP-conjugated proteins stimulated cytotoxic responses indicate that: (a) phagocytic accessory cells are required for generating cytotoxicity; (b) interaction of TNP-protein with cell surfaces was not mediated by a phagocytic mechanism; and (c) H-2 restriction is not determined by the phagocytic accessory cells. Changes in the ability to generate TNP-dependent cytotoxicity were induced by injecting mice with trinitrobenzene sulfonic acid (TNBS). The effects were dependent on TNBS dose and time after injection. Short-term priming followed by specific unresponsiveness four months later was observed.